Photosynthesis and Cellular...

Photosynthesis

8-1 Energy and Life

Copyright Pearson Prentice Hall

• All cells need energy to carry out their activities

• All energy ultimately comes from the sun

• Photosynthesis—process in which some of the

solar energy is captured by plants (producers) and

transformed into glucose molecules used by other

organisms (consumers).

6CO2 + 6H2O C6H12O6 + 6O2

Light energy

enzymes

Basics of Photosynthesis

• Glucose is the main source of energy for all life.

The energy is stored in the chemical bonds.

• Cellular Respiration—process in which a cell

breaks down the glucose so that energy can be

released. This energy will enable a cell to carry

out its activities.

C6H12O6 + 6O2 6CO2 + 6H2O + energyenzymes

Basics of Photosynthesis

Autotrophs and Heterotrophs

• Autotroph—organisms that

synthesize organic molecules

from inorganic materials (a.k.a.

producers)

– Photoautotrophs—use light

as an energy source

(plants, algae, some

prokaryotes)

• Heterotroph—organisms that

acquire organic molecules

from compounds produced by

other organisms (a.k.a.

consumers)http://www.flatrock.org.nz/topics/animals/assets/conscious_animal.jpg

Chemical Energy and ATP

• Energy comes in

many forms including

light, heat, and

electricity.

• Energy can be stored

in chemical

compounds, too.


http://www.green-the-world.net/images/forms_of_energy.jpg


• An important chemical compound that cells use

to store and release energy is adenosine

triphosphate, abbreviated ATP.

• ATP is used by all types of cells as their basic

energy source.


http://www.accessexcellence.org/RC/VL/GG/ecb/ecb_images/03_32_ATP_and_ADP_cycle.jpg

Resources/Movies/vaatpfor.mov


• ATP consists of:

– adenine

– ribose (a 5-carbon

sugar)

– 3 phosphate groups


http://dm.ncl.ac.uk/helencollard/blogger/wp-content/uploads/2009/04/atp.gif



• The three phosphate groups are the key to

ATP's ability to store and release energy.

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• Storing Energy

– ADP has two phosphate groups instead of three.

– A cell can store small amounts of energy by adding a

phosphate group to ADP.


http://zymes.com/wordpress/wp-content/uploads/2007/04/atp_sr.jpg


• Releasing Energy

– Energy stored in ATP is released by breaking the

chemical bond between the second and third

phosphates.


http://zymes.com/wordpress/wp-content/uploads/2007/04/atp_sr.jpg


• The energy from ATP is needed for many

cellular activities, including active transport

across cell membranes, protein synthesis and

muscle contraction.

• ATP’s characteristics make it exceptionally

useful as the basic energy source of all cells.


Using Biochemical Energy

• Most cells have only a small amount of ATP,

because it is not a good way to store large

amounts of energy.

• Cells can regenerate ATP from ADP as needed

by using the energy in foods like glucose.



8-1

Organisms that make their own food are called

a) autotrophs.

b) heterotrophs.

c) decomposers.

d) consumers.


8-1

Most autotrophs obtain their energy from

a) chemicals in the environment.

b) sunlight.

c) carbon dioxide in the air.

d) other producers.


8-1

How is energy released from ATP?

a) A phosphate is added.

b) An adenine is added.

c) A phosphate is removed.

d) A ribose is removed.


8-1

How is it possible for most cells to function with

only a small amount of ATP?

a) Cells do not require ATP for energy.

b) ATP can be quickly regenerated from ADP and P.

c) Cells use very small amounts of energy.

d) ATP stores large amounts of energy.


8-1

Compared to the energy stored in a molecule of

glucose, ATP stores

a) much more energy.

b) much less energy.

c) about the same amount of energy.

d) more energy sometimes and less at others.

END OF SECTION

8-2 Photosynthesis: An Overview


Photosynthesis: An Overview

• The key cellular process identified with energy

production is photosynthesis.

• Photosynthesis is the process in which green

plants use the energy of sunlight to convert

water and carbon dioxide into high-energy

carbohydrates and oxygen.


The Photosynthesis Equation

• The Photosynthesis Equation

6CO2 + 6H2O C6H12O6 + 6O2

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Light energy

enzymes

http://www.biologycorner.com/resources/photosynthesis.jpg

The Photosynthesis Equation

• Photosynthesis uses the energy of sunlight to

convert water and carbon dioxide into high-

energy sugars and oxygen.


A Photosynthesis Road Map

– Photosynthesis is composed of two

processes:

• The light reactions convert solar

energy to chemical energy.

• The Calvin cycle makes sugar from

carbon dioxide.

Figure 7.4

Light and Pigments

• In addition to water and carbon dioxide,

photosynthesis requires light and chlorophyll.

Copyright Pearson Prentice Hallhttp://www.biologycorner.com/resources/photosynthesis.jpg


Light and Pigments

• Plants gather the sun's energy with light-

absorbing molecules called pigments.

• The main pigment in plants is chlorophyll.

• There are two main types of chlorophyll:

– chlorophyll a

– chlorophyll b

Light and Pigments

• Chlorophyll absorbs light

well in the blue-violet

and red regions of the

visible spectrum.

• Chlorophyll does not

absorb light well in the

green region of the

spectrum.

• Green light is reflected

by leaves, which is why

plants look green.


Light and Pigments

• Light is a form of energy, so any compound that

absorbs light also absorbs energy from that

light.

• When chlorophyll absorbs light, much of the

energy is transferred directly to electrons in

the chlorophyll molecule, raising the energy

levels of these electrons.

• These high-energy electrons are what make

photosynthesis work.


8-2

Plants use the sugars produced in

photosynthesis to make

a) oxygen.

b) starches.

c) carbon dioxide.

d) protein.


8-2

The raw materials required for plants to carry out

photosynthesis are

a) carbon dioxide and oxygen.

b) oxygen and sugars.

c) carbon dioxide and water.

d) oxygen and water.


8-2

The principal pigment in plants is

a) chloroplast.

b) chlorophyll.

c) carotene.

d) carbohydrate.


8-2

The colors of light that are absorbed by chlorophylls

are

a) green and yellow.

b) green, blue, and violet.

c) blue, violet, and red.

d) red and yellow.

END OF SECTION

8-3 The Reactions of

Photosynthesis


Photosynthesis: redox process

• Oxidation-reduction reaction:

– Oxidation-loss of electrons from one

substance

– Reduction-addition of electrons to another

substance

6CO2 + 6H2O C6H12O6 + 6O2

Light energy

enzymes

oxidation

reduction

Releases e- (and H+ ions)

gains e- (and H+ ions)

6CO2 + 6H2O C6H12O6 + 6O2

Light energy

enzymes

oxidation

reduction



Light energy

enzymes

Light energy

enzymes

oxidation

reduction

oxidation

reduction




Inside a Chloroplast

• In plants, photosynthesis takes place inside

chloroplasts.



• Chloroplasts contain thylakoids—saclike

photosynthetic membranes.



• Thylakoids are arranged in stacks known as

grana. A singular stack is called a granum.



• Proteins in the thylakoid membrane organize

chlorophyll and other pigments into clusters

called photosystems, which are the light-

collecting units of the chloroplast.


• The light-dependent

reactions take place

within the thylakoid

membranes.

• The Calvin cycle

takes place in the

stroma, which is the

region outside the

thylakoid

membranes.



Electron Carriers

• Electron Carriers

– When electrons in chlorophyll absorb sunlight, the

electrons gain a great deal of energy.

– Cells use electron carriers to transport these high-

energy electrons from chlorophyll to other

molecules.

• One carrier molecule is NADP+.

• Electron carriers, such as NADP+, transport electrons.

• NADP+ accepts and holds 2 high-energy electrons along with

a hydrogen ion (H+). This converts the NADP+ into NADPH.


Electron Carriers

• The conversion of NADP+ into NADPH is one way

some of the energy of sunlight can be trapped

in chemical form.

• The NADPH carries high-energy electrons to

chemical reactions elsewhere in the cell.

• These high-energy electrons are used to help

build a variety of molecules the cell needs,

including carbohydrates like glucose.


Light-Dependent Reactions

• The light-dependent reactions require light.

• The light-dependent reactions produce oxygen

gas and convert ADP and NADP+ into the energy

carriers ATP and NADPH.

1. When photosystem II absorbs light an e- is excited in the

reaction center chlorophyll (P680) and gets captured by

the primary e- acceptor.

• This leaves a hole in the P680

2. To fill the hole left in P680, an enzyme extracts e- from

water and supplies them to the reaction center

• A water molecule is split into 2 H+ ions and an

oxygen atom, which immediately combines with

another oxygen to form O2

3. Each photoexcited e- passes from primary e- acceptor to

photosystem I via an electron transport chain.

• e- are transferred to e- carriers in the chain

4. As e- cascade down the e- transport chain, energy is

released and harnessed by the thylakoid membrane to

produce ATP

• This ATP is used to make glucose during Calvin cycle

5. When e- reach the bottom of e- transport chain, it fills the

hole in the reaction center P700 of photosystem I.

• Pre-existing hole was left by former e- that was

excited

6. When photosystem I absorbs light an e- is excited in the

reaction center chlorophyll (P700) and gets captured by

the primary e- acceptor.

• e- are transferred by e- carrier to NADP+ (reduction

reaction) forming NADPH

• NADPH provides reducing power for making

glucose in Calvin cycle

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html

Chemiosmosis• Energy released from ETC is

used to pump H+ ions (from the split water) from the stroma across the thylakoid membrane to the interior of the thylakoid.

– Creates concentration gradient across thylakoid membrane

– Process provides energy for chemisomostic production of ATP

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html


Light-Dependent Reactions

• The light-dependent reactions use water, ADP,

and NADP+.

• The light-dependent reactions produce oxygen,

ATP, and NADPH.

• These compounds provide the energy to build

energy-containing sugars from low-energy

compounds.


The Calvin Cycle

• The Calvin Cycle – ATP and NADPH formed by the light-dependent

reactions contain an abundance of chemical energy, but they are not stable enough to store that energy for more than a few minutes.

– During the Calvin cycle plants use the energy that ATP and NADPH contain to build high-energy compounds that can be stored for a long time.

•

The Calvin Cycle

• The Calvin cycle uses

ATP and NADPH from the

light-dependent

reactions to produce

high-energy sugars.

• Because the Calvin cycle

does not require light,

these reactions are also

called the light-

independent reactions.


Resources/Movies/vacalvin.mov

The Calvin Cycle

• Six carbon dioxide molecules enter the cycle

from the atmosphere and combine with six 5-

carbon molecules.


The Calvin Cycle

• The result is twelve 3-carbon molecules, which

are then converted into higher-energy forms.


The Calvin Cycle

• The energy for this conversion comes from ATP

and high-energy electrons from NADPH.


The Calvin Cycle

• Two of twelve 3-carbon molecules are removed

from the cycle.


The Calvin Cycle

• The molecules are used to produce sugars,

lipids, amino acids and other compounds.

The Calvin Cycle

•The 10 remaining 3-carbon molecules are

converted back into six 5-carbon molecules,

which are used to begin the next cycle.

The Calvin Cycle

• The two sets of photosynthetic reactions work

together.

– The light-dependent reactions trap sunlight energy

in chemical form.

– The light-independent reactions use that chemical

energy to produce stable, high-energy sugars from

carbon dioxide and water.


The Calvin Cycle

• Factors Affecting Photosynthesis – Many factors affect the rate of photosynthesis,

including:

• Water

• Temperature

• Intensity of light


How Photosynthesis Moderates Global

Warming

• Photosynthesis has an enormous impact on the

atmosphere.

– It swaps O2 for CO2.

http://www.destination360.com/asia/malaysia/images/s/borneo-rainforest.jpg

How Photosynthesis Moderates Global

Warming

• Greenhouses used to grow plant indoors

– Trap sunlight that warms the air inside.

• A similar process, the greenhouse effect,

– Warms the atmosphere.

– Is caused by atmospheric CO2.

Global Warming

• Greenhouse gases (CO2,

CH4, CFC’s) are the most

likely cause of global

warming, a slow but

steady rise in the Earth’s

surface temperature.

– Destruction of forests may

be increasing this effect.

– Combustion of fossil fuels

Global Warming Consequences

• Polar ice caps melting

• Rise in sea level and

flooding of current

coastline

– New York, Miami, Los

Angeles underwater

• Change in types of

plants—more adapted to

warmer temps. and less

waterhttp://i.treehugger.com/images/2007/10/24/melting%20ice-jj-002.jpg


8-3

In plants, photosynthesis takes place inside the

a) thylakoids.

b) chloroplasts.

c) photosystems.

d) chlorophyll.


8-3

Energy to make ATP in the chloroplast comes most

directly from

a) hydrogen ions flowing through an enzyme in the thylakoid

membrane.

b) transfer of a phosphate from ADP.

c) electrons moving through the electron transport chain.

d) electrons transferred directly from NADPH.


8-3

NADPH is produced in light-dependent reactions and carries energy in the form of

a) ATP.

b) high-energy electrons.

c) low-energy electrons.

d) ADP.


8-3

What is another name for the Calvin cycle?

a) light-dependent reactions

b) light-independent reactions

c) electron transport chain

d) photosynthesis


8-3

Which of the following factors does NOT directly affect

photosynthesis?

a) wind

b) water supply

c) temperature

d) light intensity

END OF SECTION

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